The biosynthesis of eukaryotic cell membranes is being explored using new immunochemical and immunocytochemical techniques. The techniques are being applied to the study of rod outer segment membrane biosynthesis in photoreceptor cells of the retina. Electron microscopic localization of opsin and a recently describe large protein in rod outer segment membranes has been accomplished using thin sections of retinas embedded in cross-linked bovine serum albumin. Preliminary results suggest localization of newly synthesized opsin in Golgi apparatus. Opsin is also localized in rod outer segments as expected. Antibodies to frog opsin purified in a cattle opsin immunoabsorbant react both with frog rod outer segments and cone proteins. Antibodies to the large protein of frog rod outer segments localize this protein to the incisures and edges of disc membranes. This is the first reported localization of a minor intrinsic membrane component to such a subcellular site in the rod outer segment. In order to increase the sensitivity of immunocytochemical techniques we are extending the approach to frozen sucrose embedded tissues. Antigens are currently being localized with specific antibody F(ab')2 fragments. Second step reagents have been ferritin labeled antibody. New alternative reagents are being investigated. Biotin will be covalently coupled to specific antibodies and the bound biotin-ab complex will be detected with avidin-ferritin or avidin-hemocyanin. Display of antigens on the cell surfaces will be investigated by high resolution scanning electron microscopy.